JPH04356734A - Control method for optical head - Google Patents

Abstract

PURPOSE:To detect the position of an optical head, and besides, to detect laser power too by using reflected excess light generated inevitably in a polarizing beam splitter (SBS) 17. CONSTITUTION:A P wave from a semiconductor laser 11 becomes incident upon the plarizing beam splitter (SBS) 17. The SBS 17 reflects a part of the P wave and transmits a part of the same. This transmitted light is used for reading a magneto-optical memory by a usual method. The P wave reflected by the SBS 17 becomes incident upon a beam splitter (BS) 43 and its reflected light becomes incident upon a position sensor 51 and detects the position of the optical head. The transmitted light of the BS 43 becomes incident upon a photodiode 45 and detects the power of the laser 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the position of an optical head used in magneto-optical recording, etc., in which information is read by irradiating a recording medium with linearly polarized light, and a method for controlling the intensity of light emitted from the optical head.

0002

[Prior Art] In magneto-optical recording, a recording medium is irradiated with linearly polarized light from a coherent light source such as a laser using an optical head, and the direction of rotation of the plane of polarization of this reflected light based on the direction of magnetization of the recording medium (Kerr effect ) is detected and the information is read out. The position of the optical head with respect to the recording medium is controlled by counting the number of recording tracks crossed by a light spot from the optical head or by directly detecting the position of the optical head. When directly detecting the position of the optical head, there are generally two methods: one uses an external scale and a separate light source, and the other uses a separate light source and a position sensor such as a photodiode array. However, in these cases, since the light source is a separate light source, the number of parts increases, and since it is difficult to convert the light from the separate light source into parallel light, there are restrictions on the installation location. Furthermore, in the case of using an external scale and a separate light source, there is a problem in that it is expensive and increases the cost of the entire device.

[0003] Also, as a method of controlling the intensity change of a laser, which is a light source, there is a known method of controlling the output of a laser diode using a photodiode built into the laser diode. However, in this method, the reflected light from the recording medium returns to some extent into the laser diode, making the laser oscillation unstable and making accurate control impossible.

Furthermore, in current optical heads, particularly in magneto-optical recording and reproducing optical heads, a portion of the light beam from the laser is reflected by the beam splitter and leaks out of the recording and reproducing system, so this surplus light is utilized. It is also known to control the output by detecting the intensity of laser light. but,
It is not known to utilize this surplus light to detect the position of an optical head.

[0005]

[Problems to be Solved by the Invention] The present invention utilizes a portion of the light used for recording and reproducing information, and can improve the position of the optical head or A method for controlling light source intensity is provided.

[0006]

[Means for Solving the Problems] The optical head control method of the present invention is such that a coherent light beam such as a laser beam is incident on a beam splitter having polarization characteristics and reflected or transmitted, thereby recording and/or reproducing information. In this optical head control method, out of the light beams separated and emitted by the beam splitter, surplus light beams that are not involved in recording/reproducing information are used to control the position of the optical head and the intensity of the light beam incident on the beam splitter (i.e., the laser beam). oscillation intensity). The position control of the optical head is
This surplus luminous flux is taken out and detected. On the other hand, the intensity of the light flux incident on the beam splitter may be detected and controlled inside the optical head using a portion of the surplus light flux, or may be detected and controlled by extracting the surplus light flux to the outside.

[0007]

[Embodiment] FIG. 1 is an explanatory top view showing an optical system (optical head) according to an embodiment of the present invention, and FIG. 2 is a side view thereof.
FIG. 3 is an explanatory diagram of the entire system. Note that the objective lens 23 and the magneto-optical disk 53 are not shown in FIG. 1, and the semiconductor laser 11 and the collimator lens 1 are not shown in FIG.
3 is omitted from illustration.

The optical head 39 includes a semiconductor laser 11, a collimator lens 13, a shaping prism 15,
Polarizing beam splitter (SBS) 17, rising mirror 2
1. Objective lens 23, 1/2 wavelength plate 25, condenser lens 2
7, cylindrical lens 29, polarizing beam splitter (PBS) 31, information detection photodiode 33,3
5, an iris 41, a beam splitter 43, and a power detection photodiode 45 are built in, and are driven in the direction of arrow A in FIGS. Corresponds to the tracking direction (diameter direction).

The laser beam oscillated from the semiconductor laser 11 is linearly polarized, and a polarizing beam splitter (SBS)
It is arranged so that it becomes a P wave with respect to the prism incidence surface of No. 17. The laser beam is turned into a parallel beam by the collimator lens 13 and enters the SBS 17 . The SBS 17 separates the light flux incident on the magneto-optical disk 53 and the magneto-optical disk 53.
In order to effectively separate the emitted light beam that is reflected by the surface and contains the information signal component, the S-wave component (Kerr effect component) is reflected 100%, while the P-wave component is partially transmitted and partially reflected (
For example, it is designed to be 50% at a time).

Fifty percent of the P wave incident on the SBS 17 is transmitted, raised by the raising mirror 21, converged by the objective lens 23, and irradiated with a spot onto the magneto-optical disk 53. The irradiated linearly polarized light of the P-wave component is rotated according to the recorded information (direction of magnetization) on the disk 53, and is reflected as light containing the S-wave component (signal). This reflected light enters the SBS17 again, and 100% of the S wave component
50% of the P-wave component is reflected, and the S-wave component is guided to the 1/2 wavelength plate 25 to rotate the polarization, and the condensing lens 27,
After passing through a cylindrical lens 29, it is divided into two orthogonal polarization components by a normal polarization beam splitter 31.
The information is guided to information detection photodiodes 33 and 35, and information is read out as a difference signal between the outputs.

As mentioned above, since the SBS 17 reflects a part of the P wave, a part of the laser light (P wave) that is made into a parallel beam by the collimator lens 13 and incident on the SBS 17 is
The light is reflected outside the information signal detection system at the BS 17 and becomes surplus light. This surplus light has a power of about 0.5 mW, for example, and has sufficient intensity for position detection by the sensor and for monitoring the power detection of the semiconductor laser 11. Therefore, in the present invention, the position of the optical head 39 (objective lens 23) is detected, or the oscillation intensity of the semiconductor laser 11 is further detected by utilizing the fact that this surplus light is a parallel light flux and has sufficient power. to perform power control.

The reflected light that passes through the collimator lens 13 and becomes a parallel light beam and is reflected by the SBS 17 is focused by the iris 41 and enters the beam splitter 43 . A portion of this light is reflected by the beam splitter 43 and guided out of the optical head 39 through the opening of the housing 37, and enters the position sensor 51, where the position of the optical head 39 is detected. As a position sensor,
A photodiode array can be used, and if the resolution and speed are within acceptable range, a CCD (charge-coupled device) can be used.
etc. can also be used.

Further, a part of the parallel light beam incident on the beam splitter 43 is transmitted therethrough and is incident on a detection photodiode 45 mounted on the optical head 39. Thereby, the oscillation intensity of the semiconductor laser 11 can be detected and controlled.

FIGS. 4 to 6 show other embodiments of the present invention and are explanatory diagrams corresponding to FIGS. 1 to 3. In this embodiment, the P wave, which is made into a parallel beam by the collimator lens 13 and reflected by the SBS 17, is guided to the position sensor 51, and the position sensor 51 outside the optical head detects the position of the optical head 39 and the semiconductor laser 1.
This embodiment is the same as the previous embodiment except that both oscillation intensities of 1 are detected. 47 indicates a reflecting mirror. Position sensors such as photodiode arrays and CCDs exhibit linearity in the current (charge) generated with respect to the amount of incident light.
The oscillation intensity of 1 can be detected.

Furthermore, in each of the above embodiments, the same effects can be obtained even if half mirrors exhibiting similar polarized light reflection/transmission characteristics are used.

[0016]

According to the present invention, the position of the optical head or even the intensity of the laser beam can be detected by using the surplus light of the laser beam used for the optical information signal.
Since collimated parallel light can be used, compact and highly accurate detection is possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory top view showing an optical system (optical head) according to an embodiment of the present invention.

FIG. 2 is a side view of FIG. 1;

FIG. 3 is an explanatory diagram of the entire control system using the optical system shown in FIGS. 1 and 2. FIG.

FIG. 4 is an explanatory top view showing an optical system (optical head) according to another embodiment of the present invention.

FIG. 5 is a side view of FIG. 4;

FIG. 6 is an explanatory diagram of the entire control system using the optical system shown in FIGS. 4 and 5. FIG.

[Explanation of symbols]

11 Semiconductor laser 13 Collimator lens 15 Shaping prism 17 Polarizing beam splitter (SBS) 21 Raising mirror 23 Objective lens 25 1/2 wavelength plate 27 Condenser lens 29 Cylindrical lens 31 Polarizing beam splitter (PBS) 33 Photodiode for information signal detection 35 Information signal detection photodiode 41 Iris 43 Beam splitter 45 Power detection photodiode 47 Reflection mirror 51 Position sensor 53 Magneto-optical disk

Claims (2)

[Claims] 1. In an optical head that records and/or reproduces information by inputting a coherent light beam such as a laser beam to a beam splitter having polarization characteristics and causing the beam splitter to reflect or transmit the light beam, the beam splitter separates and outputs the light beam. Among them, a part of the surplus light flux that is not related to information recording/reproduction is taken out to the outside of the optical head to detect the position of the optical head, and the remaining part of the surplus light flux is used to reduce the light flux that enters the beam splitter. 1. A method for controlling an optical head, the method comprising controlling the intensity of the optical head. 2. In an optical head that records and/or reproduces information by inputting a coherent light beam such as a laser beam into a beam splitter having polarization characteristics and causing it to be reflected or transmitted, the beam splitter separates and outputs the beam. Of these, surplus light flux not related to information recording/reproduction is taken out to the outside of the optical head to detect the position of the optical head, and the surplus light flux is used to control the intensity of the light flux incident on the beam splitter. A method of controlling an optical head.